Efect of hybrid steel fiber use on the shear behavior of beams containing ultra high performance concrete

Ultra High Performance Concrete (UHPC) is a new generation concrete with superior mechanical properties compared to conventional concretes. UHPC has very high compressive strength and durability compared to conventional concrete due to the use of ultra fine materials and the low water to binder ratio. Existing studies have demonstrated the contribution of UHPC to shear strength of reinforced concrete beams as a result of its high strength, deformation capacity and cracking control under tension. In addition, although the advantages of using different types of fibers together as hybrid form due to the synergistic effect over the use of single fiber type have been revealed in many material-based studies, studies on the hybrid fiber use in structural members are very limited. In this study, the effect of the hybrid steel fiber use on the shear behavior of I-section reinforced concrete beams produced with UHPC was investigated with an experimental campaign consisting of two stages. In the first stage, the effect of hybrid steel fiber use on the basic mechanical properties was investigated with the material-based tests. In the second stage, in order to evaluate the shear behavior, I-section reinforced concrete beams were produced using UHPC mixtures with mono and hybrid steel fibers and tested under shear effective loading. The results showed that the compressive and splitting tensile strengths increased with increasing fiber content. The best performance in terms of flexural tensile strength of UHPC mixtures was obtained with the use of 2.0% mono fiber by volume. As a result of the tests of I-section beams, it was observed that the use of steel fibers significantly increased the shear strength, while shear failure could be prevented with the use of 2.0% fiber by volume. As a result of the experimental study, no significant advantage of the hybrid fiber use could be determined in terms of examined parameters.